The present invention generally relates to overhead transport (OHT) vehicles in an automatic material handling system (AMHS) and more particularly, to a safety system which prevents OHT vehicles from striking and injuring facility personnel during loading and unloading of cassette pods at the load ports of semiconductor processing tools.
In the manufacturing of a product, the product is usually processed at many work stations or processing machines. The transporting or conveying of partially-finished products, or work-in-process (WIP) parts, is an important aspect in the total manufacturing process. The careful conveying of semiconductor wafers is especially important in the manufacturing of integrated circuit chips due to the delicate nature of the chips. Furthermore, in fabricating an IC product, a multiplicity of fabrication steps, i.e., as many as several hundred, is usually required to complete the fabrication process. A semiconductor wafer or IC chip must be transported between various process stations in order to facilitate various fabrication processes.
For instance, to complete the fabrication of an IC chip, various steps of deposition, cleaning, ion implantation, etching, and passivation must be carried out before an IC chip is packaged for shipment. Each of these fabrication steps must be performed in a different process machine, i.e., a chemical vapor deposition chamber, an ion implantation chamber, an etcher, etc. A partially processed semiconductor wafer must be conveyed between various work stations many times before the fabrication process is completed. The safe conveying and accurate tracking of such semiconductor wafers or work-in-process parts in a semiconductor fabrication facility is therefore an important aspect of the total fabrication process.
Conventionally, partially finished semiconductor wafers or WIP parts are conveyed in a fabrication plant by automatically-guided vehicles (AGVs) or overhead transport vehicles (OHTs) that travel on predetermined routes or tracks. For the conveying of semiconductor wafers, the wafers are normally loaded into cassettes or SMIF (standardized mechanical interface) pods and then picked up and placed in the automatic conveying vehicles. For identifying and locating the various semiconductor wafers or WIP parts being transported, the cassettes or pods are normally labeled with a tag positioned on the side of the cassette or pod. The tags can be read automatically by a tag reader that is mounted on the guard rails of the conveying vehicle. The AGVs and OHTs normally transport the pods from bay to bay along an interbay loop, and eventually deliver the pods to a robotic storage house, or xe2x80x9cstockerxe2x80x9d, which automatically delivers the pods to an intrabay loop. The AGVs and OHTs also deliver the pods to processing tools and inspection tools.
In modern semiconductor fabrication facilities, OHTs are typically not used to place cassettes containing 8-inch diameter wafers in the tool load ports. Rather, these cassettes are usually placed in the load port manually. On the other hand, cassettes containing 12-inch diameter wafers are heavier (about 8.9 kg when loaded with 25 wafers). Consequently, automatic guided vehicles (AGV) and overhead transport vehicles (OHT) are extensively used to load and unload these cassettes to and from the tool load and unload ports. The AGV and OHT utilize the input/output ports of a processing tool or inspection tool to load or unload wafer lots, i.e., normally stored in SMIF pods. A perspective view of a standard overhead transport vehicle system 10 is shown in FIG. 1.
In the OHT system 10 of FIG. 1, multiple vehicles 12, two of which are shown, travel on a common track 14. Both a load port 18 and an unload port 20 are provided on the tool 16. As the OHT vehicle 12 stops at the position for unloading a SMIF pod 22 into the load port 18, a gripper 15 holding the pod 22 extends downwardly from the vehicle 12 to position the pod 22 in the load port 18. After processing, another vehicle 12 removes the pod 22 from the unload port 20.
Frequently, facility personnel perform various tasks in the area surrounding the tool 16. During loading of the pods 22, the vehicles 12, and particularly the downwardly-extending grippers 15 thereof, as well as the pod 22 carried by the grippers 15, have a tendency to strike and injure the personnel. Accordingly, a device is needed for sensing personnel or other obstructing objects in the vicinity of the load port of a processing tool, inspection tool or stocker and terminating loading of cassettes or pods into the tool or stocker in order to prevent striking of and injury to the personnel.
An object of the present invention is to provide a safety system which may be used to prevent injury to personnel in the vicinity of a processing tool, inspection tool or stocker during loading of wafer cassettes into the tool or stocker.
Another object of the present invention is to provide a safety system which may be used to sense the presence of obstructions in the path of an overhead transport (OHT) vehicle and temporarily stop further loading operation of the OHT in order to prevent injury to personnel.
Still another object of the present invention is to provide a safety system which may include an overhead sensor provided on an OHT, a safety panel or panels provided on a processing tool, inspection tool or stocker and/or a light curtain provided on the tool or stocker to prevent or at least reduce the likelihood of injury to personnel during loading of wafer cassettes into a tool or stocker in a semiconductor fabrication facility.
Yet another object of the present invention is to provide a safety system which may integrate emergency stop signals from an overhead sensor provided on an OHT and from a light curtain provided on a processing tool, inspection tool or stocker to terminate further loading of a wafer cassette or pod into a processing tool or stocker in the event of the presence of an obstruction in the travel path of the wafer cassette or pod.
A still further object of the present invention is to provide a safety system which is capable of routing OHT overhead sensor function from an overhead OHT sensor to a light curtain on a tool or stocker in the event that a component on the tool or stocker interferes with the look-down sensing function of the overhead OHT sensor.
In accordance with these and other objects and advantages, the present invention is generally directed to a safety system for an overhead transport vehicle (OHT). In one embodiment, the safety system may include a pair of safety panels provided on opposite sides of the load and unload ports on a tool or stocker. An overhead sensor is provided on the OHT and is operably connected to a light curtain on the tool. In the event that the overhead sensor detects an obstruction in the travel path of the OHT during loading of a pod or cassette into the tool or stocker, the light curtain transmits an emergency stop signal to the tool or stocker controller, which terminates further loading operation of the OHT. In another embodiment, the light curtain assumes the look-down sensing function of the overhead sensor in the event that tool components, such as a front control panel, for example, interfere with the look-down function of the overhead sensor.